Racial and genetic determinants of plasma factor XIII activity.

Factor XIII (F XIII), a plasma transglutaminase, is essential for normal hemostasis and fibrinolysis. Plasma F XIII consists of two catalytic A (F XIIIA) and two non-catalytic B (F XIIIB) subunits. Activated F XIII is involved in the formation of fibrin gel by covalently crosslinking fibrin monomers. As the characteristics of the fibrin gel structure have been shown to be associated with the risk of coronary heart disease (CHD), F XIII activity may play a seminal role in its etiology. In this investigation, we determined plasma F XIII activity in two racial groups, including Asian Indians (n = 258) and Chinese (n = 385). Adjusted plasma F XIII activity was significantly higher in Indian men (142 vs. 110%; P < 0.0001) and women (158 vs. 111%; P < 0.0001) than their Chinese counterparts. As compared to Indians where the distribution of F XIII activity was almost normal, in Chinese it was skewed towards low activity. In both racial groups, bivariate and multivariate analyses showed strong correlation of F XIII activity with plasma fibrinogen and plasminogen levels. Race explained about 25% of the variation in F XIII activity even after the adjustment of significant correlates. We also determined the contribution of common genetic polymorphisms in the F XIIIA and F XIIIB genes in affecting plasma F XIII activity. Both loci showed significant and independent effects on plasma F XIII activity in Indians (F XIIIA, P < 0.01; F XIIIB, P < 0.05) and Chinese (F XIIIA, P < 0.0001; F XIIIB, P < 0.13) in a gene dosage fashion. This study shows that both racial and genetic components play a significant role in determining plasma F XIII activity, and consequently it may affect the quantitative risk of CHD. Genet. Epidemiol. 19:440–455, 2000. © 2000 Wiley-Liss, Inc.